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<title>Problem 1674. -- [Usaco2005]Part Acquisition -- 衡阳八中OJ离线版-2012-02-29</title><center><h2>1674: [Usaco2005]Part Acquisition</h2><span class=green>Time Limit: </span>5 Sec&nbsp;&nbsp;<span class=green>Memory Limit: </span>64 MB<br><span class=green>Submit: </span>120&nbsp;&nbsp;<span class=green>Solved: </span>43<br>[<a href='submitpage.php?id=1674'>Submit</a>][<a href='problemstatus.php?id=1674'>Status</a>][<a href='bbs.php?id=1674'>Discuss</a>]</center><h2>Description</h2><div class=content>The cows have been sent on a mission through space to acquire a new
milking machine for their barn.  They are flying through a cluster
of stars containing N (1 <= N <= 50,000) planets, each with a trading
post.

The cows have determined which of K (1 <= K <= 1,000) types of
objects (numbered 1..K) each planet in the cluster desires, and
which products they have to trade. No planet has developed currency,
so they work under the barter system: all trades consist of each
party trading exactly one object (presumably of different types).

The cows start from Earth with a canister of high quality hay (item
1), and they desire a new milking machine (item K). Help them find
the best way to make a series of trades at the planets in the cluster
to get item K.  If this task is impossible, output -1.

</div><h2>Input</h2><div class=content>* Line 1: Two space-separated integers, N and K.

* Lines 2..N+1: Line i+1 contains two space-separated integers, a_i
        and b_i respectively, that are planet i's trading trading
        products. The planet will give item b_i in order to receive
        item a_i.

</div><h2>Output</h2><div class=content>* Line 1: One more than the minimum number of trades to get the
        milking machine which is item K (or -1 if the cows cannot
        obtain item K).
</div><h2>Sample Input</h2>
			<div class=content><span class=sampledata>6 5   //6个星球,希望得到5,开始时你手中有1号货物.<br />
1 3   //1号星球,希望得到1号货物,将给你3号货物<br />
3 2<br />
2 3<br />
3 1<br />
2 5<br />
5 4<br />
</span></div><h2>Sample Output</h2>
			<div class=content><span class=sampledata>4<br />
<br />
<br />
OUTPUT DETAILS:<br />
<br />
The cows possess 4 objects in total: first they trade object 1 for<br />
object 3, then object 3 for object 2, then object 2 for object 5.</span></div><h2>HINT</h2>
			<div class=content><p></p></div><h2>Source</h2>
			<div class=content><p><a href='problemset.html?search=Silver'>Silver</a></p></div><center>[<a href='submitpage.php?id=1674'>Submit</a>][<a href='problemstatus.php?id=1674'>Status</a>][<a href='bbs.php?id=1674'>Discuss</a>]</center>﻿<br>

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